I was using a sandy-bridge i5 and it seemed only support 2 screen output. So I tried to insert an independent graphic card which supports 3-screen output. But the hw acceleration for h.264 encoding and decoding is not capable if I use the independent graphic card. How to solve it?
Intel's HW acceleration for encoding (Quick Sync Video) is a feature of Intel's display adapter device (GPU). Any application requesting Intel acceleration needs make sure it is configured to make use of Intel's device ( driver and hardware ) and not the independent (descrete) graphics card. Please see the Intel Media SDK Developer Guide (https://software.intel.com/sites/default/files/article/265550/intel-mediasdk-2013-developers-guide.pdf) section 4.17 for information about handling multiple graphics adapters.